Generally, digital conference arrangements sum information samples representing, for example, speech from each conferee and then distribute the resulting sample to each conference port. One such arrangement is described in the parent application of M. A. Marouf and P. W. Vancil in which only samples from selected ports are included in a resulting output sample to reduce noise, echo, and other types of distortion. The selection process is accomplished by assigning each port a priority level based on the state of the port in each one of two sets of states and summing the information samples of only those ports having the highest priority levels. One set of states may comprise the levels of speech detected on the port, whereas the other set may comprise the history of activity on the port such as, for example, how long the conferee has been silent, the interval between speech bursts, etc.
In many prior art arrangements, a port is commonly held over or placed in a holdover state for a fixed time interval between words to reduce speech clipping. Generally, such fixed time interval arrangements are unable to discriminate between speech and extraneous noise conditions such as, for example, the rustling of papers. Hence, a port that was activated by noise may be placed in the same holdover state as a port that was activated by speech, thereby preempting other conferees in a speaker selection process.
In contrast, when no holdover is performed and all of the conferees are silent, nothing is heard on the conference bridge. This is annoying as the conferee has the feeling that he is cut off from the conference.